1. Field of the Invention
The invention relates generally to bipolar articles, such as batteries, and in particular to bipolar articles having interpenetrating current collectors and/or arbitrary form factors that are useful, e.g., for integral formation or embedding in various electronic devices.
2. Summary of the Related Art
Batteries, and particularly rechargeable batteries, are widely used in a variety of devices such as cellular telephones, laptop computers, personal digital assistants, and toys. One example of a rechargeable battery is a lithium solid polymer electrolyte rechargeable battery. This battery can be charged by applying a voltage between the battery's electrodes, which causes lithium ions and electrons to be withdrawn from lithium hosts at the battery's cathode. Lithium ions flow from the cathode to the battery's anode through a polymer electrolyte, and are reduced at the anode, with the overall process requiring energy. Upon discharge, the reverse occurs: lithium ions and electrons are allowed to re-enter lithium hosts at the cathode, while lithium is oxidized to lithium ions at the anode. This is an energetically favorable process that drives electrons through an external circuit, thereby supplying electrical power to a device to which the battery is connected.
Currently available batteries typically have a layered design. Manufacturing constraints generally limit the available shapes or form factors of these batteries. Common form factors include cylinders, button cells (thin discs), relatively thick (>3 mm) prismatic forms, and relatively thin (<0.5 mm) prismatic forms. The relatively thick prismatic forms typically are made by rolling and pressing long coated cathode and anode electrode assemblies separated by a thin separator, or by stacking or laminating layers of cathode/electrolyte/anode material. Some of these prismatic forms are made using a jelly roll or pressed cylinder process. The relatively thin (<0.1 mm) prismatic forms are generally made using thin film processes such as physical vapor deposition.
The energy density of these currently available batteries is relatively low, due to poor volumetric utilization of space within devices in which the batteries are used. For example, short diffusion distances are required for lithium ion transport in a lithium battery. Therefore, the distances between current collectors in a multi-laminate battery structure is small, e.g., less than about 250 μm. The large number of current collectors reduces the volume and weight fractions of electroactive material in the battery. In addition, extra components generally are needed in the devices in which the batteries are used, in order to allow the batteries to be inserted and connected. Such components include an internal chamber with suitable fit and finish for consumer use, an extra set of interconnects to attach the battery to the device, and additional parts to allow the battery to be exchanged, such as, e.g., a battery cover.
Therefore, a need exists for alternative battery designs that allow for more efficient use of space within electronic devices, and thus provide improved power and energy densities.
Recently “three-dimensional batteries” have been proposed, which have anodes and cathodes with active surface areas exposed in three dimensions. Such structures potentially can improve upon the results obtained using standard battery geometries by allowing for more optimal use of materials through independent variation of the ionic and electronic transport path lengths within the device. The present invention provides advances within the emerging field of three-dimensional batteries.